The subject invention relates generally to a method and apparatus for testing the pressure integrity of blowout preventer systems which are used to control the flow of high pressure fluids from a well. More particularly, the subject relates to a blowout preventer test tool that enables a tool operator to test the pressure integrity of various size blowout preventers without removing the test tool from a well between tests. More particularly still, the subject invention relates to a blowout preventer test tool that enables a tool operator to test the pressure integrity of variable bore rams against different size pipe without removing the test tool from a well between tests. More particularly still, the subject invention relates to a blowout preventer test tool which allows a well to be safely and efficiently shut in should a xe2x80x9ckickxe2x80x9d be experienced during testing operations.
During the drilling of oil and gas wells, the hazard of a sudden and violent expulsion of fluids, often referred to as a xe2x80x9cblowout,xe2x80x9d is always present where wells are drilled into porous and permeable rocks containing pressurized gas, oil, and water. Blowouts are extremely dangerous to human life, and can cause extensive damage to property. Furthermore, blowouts waste time, money, and formation pressure needed to commercially raise oil and gas from an underground reservoir to the surface.
During the drilling process, the primary mechanism for preventing a well from xe2x80x9cblowing outxe2x80x9d is the hydrostatic pressure imparted on the exposed formation(s) in the well by a column of fluid, typically drilling mud, contained within the well bore. Ideally, this hydrostatic pressure should be roughly equivalent to the pore pressure of said formation(s), resulting in a balanced system. In the event that such hydrostatic pressure is insufficient, the high pressure gas and liquids contained within said formation(s) can invade the well bore and displace drilling fluid from the well. This phenomenon is commonly known as a xe2x80x9ckick.xe2x80x9d If prompt corrective action is not taken at the first indication of a kick, control of the well can be lost and a blowout can occur.
Blowout prevention systems have been developed to protect against the uncontrolled flow of fluids from a well. Blowout prevention systems provide a means of shutting in a well at or near the surface of the well in order to gain control of a kick before it becomes a blowout. A typical blowout preventer system or xe2x80x9cstackxe2x80x9d typically consists of a number of individual blowout preventers, each designed to seal the well bore and withstand pressure from the formation.
Drilling operations conducted from moveable drilling rigs such as drill ships, semi-submersible rigs and certain jack-up rigs differ from operations conducted from platform-supported drilling rigs in many respects. Among these differences is the location of the blowout preventer and wellhead assemblies. When drilling from drill ships, semi-submersible rigs and certain jack-up rigs, the blowout preventer and wellhead assemblies are not located on the drilling rig, but rather on the sea floor; as a result, specialized equipment known as xe2x80x9csubseaxe2x80x9d blowout preventers and wellheads are utilized. A large diameter, flexible pipe known as a riser is used to connect the subsea assemblies to the offshore rig. During drilling operations, drill pipe and other downhole equipment is lowered from the rig through the riser, as well as through the subsea blowout preventer assembly and wellhead, and into the hole which is being drilled.
Although there are numerous different types of blowout preventers, one very common variety is the ram-type blowout preventer. Ram preventers utilize sets of large, opposing piston-like elements (rams) which can be selectively closed to seal off a well bore. Pipe rams can be used to seal a well when drill pipe is in use by closing around the pipe and sealing off the annulus formed between the outer surface of the drill pipe and the inner surface of the well. Blind rams can be used to completely seal off a well bore when no pipe is in use. In very extreme cases, shear rams can also be used to completely cut through drill pipe in the well and seal off the well.
Because pipe rams form a seal around the outer surface of drill pipe, the rams must generally be designed to close around a particular size of drill pipe. For example, pipe rams which are designed to be used with 5-inch outer diameter drill pipe are specifically designed to accommodate only that size pipe; such rams will generally not form a seal around pipe having a larger or smaller outer diameter. Additionally, specialized rams known as variable bore rams exist which can be used to form a seal around different size drill pipe within a given range of pipe diameters.
Although certain wells can be drilled using a single size drill pipe, it is very common to use a tapered drill string in the drilling process. The term xe2x80x9ctapered drill stringxe2x80x9d refers to a drill string which consists of larger diameter drill pipe in one portion of a well, and smaller diameter drill pipe in another portion of said well. By way of example, a typical tapered drill string might involve the simultaneous use of both 5-inch outside diameter drill pipe, as well as 3xc2xd-inch outside diameter drill pipe in the same well. As such, a blowout preventer system utilized in connection with such a tapered drill string must be capable of sealing off the annular space around both the larger and the smaller drill pipe size.
Because blowout preventer systems are generally considered emergency equipment, active blowout preventer systems must be frequently checked and pressure-tested to ensure that they remain in good working condition. In many instances, governmental regulations require frequent testing of blowout preventer equipment. In order to accomplish such testing on subsea blowout preventer assemblies, a tubular test tool is typically coupled to a drill pipe string or other work string and lowered from the drilling rig to the blowout preventer assembly which is located on the sea floor. First, a test plug at the base of the test tool is seated within a well head assembly which is located immediately below the blowout preventer assembly. Thereafter, a selected blowout preventer is individually closed to form a seal around the outer surface of the tubular test tool, thereby creating an enclosed zone between the test plug and the closed blowout preventer. High pressure fluid is thereafter introduced into the enclosed zone created between the test plug and the blowout preventer in order to test the pressure integrity of said blowout preventer. This process is then repeated to test the other blowout preventers of the blowout preventer assembly. After all blowout preventers of a particular size have been tested, the entire test tool must generally be pulled out of the well, and a different size test tool must be run into the well before another size blowout preventer can be tested in the same manner.
It is important to note that in a subsea application, blowout preventers can be located several thousand feet below a drilling rig. For this reason, tripping a test tool in and out of a well via drill pipe often requires a significant amount of time to accomplish. Because drilling rigs are typically contracted on the basis of a xe2x80x9cdaily ratexe2x80x9d, the more time required to perform operations, including blowout preventer testing operations, the more expensive a particular drilling project becomes. As such, there is a need to conduct blowout preventer tests in an efficient manner, and to minimize the number of pipe trips required to conduct such test blowout preventers.
Several inventions have been directed toward providing a test tool for blowout preventer assemblies. U.S. Pat. No. 4,090,395 to Dixon et al. discloses an apparatus which can be used for testing both blowout preventers and wellhead casing hanger seals. The apparatus disclosed in Dixon includes a tubular member which is equipped with a means for sealing off a casing hanger opening. To operate the test tool disclosed in Dixon, a tubular member is lowered into and through a wellhead so that sealing means can be employed to seal off a casing hanger. A blowout preventer is closed to create an annular chamber between the blowout preventer to be tested and the casing hanger. The pressure integrity of the blowout preventer can then be tested by introducing high pressure fluid into this annular chamber. The apparatus disclosed in Dixon is limited to testing against single size diameter pipe strings, and does not provide a means for safely and efficiently controlling the well should a kick be experienced during the testing procedure.
U.S. Pat. No. 4,018,276 to Bode discloses a blowout preventer test plug which comprises two cylindrical bodies positioned on a tubular extension, with each cylindrical body having fluid passage ports therethrough. When the two cylindrical bodies are moved into contact, said fluid passage ports are closed and a seal is created between the tubular extension and the inner diameter of the wellhead bore. The blowout preventer tool disclosed in Bode cannot be used to test against various size pipe strings, nor does it allow an operator to safely and efficiently shut in the well, if necessary.
U.S. Pat. No. 4,881,598 to Stockinger, et al, discloses a subsea blowout preventer test apparatus which permits testing of two different size blowout preventers on a single pipe trip. The test apparatus disclosed in Stockinger includes an inner elongated cylindrical testing mandrel which is telescopingly received within a larger outer elongated cylindrical testing mandrel. A releasable locking means is provided for releasably locking the testing mandrels in a telescopingly extended position so that the blowout preventer system can first be tested against the inner testing mandrel. Thereafter, said testing mandrels can be shifted into a telescopingly collapsed position such that the blowout preventer system can also be tested against the larger diameter outer testing mandrel. Although the testing apparatus disclosed in Stockinger may permit the testing of two different size blowout preventers in a single pipe trip, it does not permit such testing on two cylindrical mandrels having similar or very close outer diameters. By way of example, the apparatus described in Stockinger cannot accommodate the testing of blowout preventers against both 5xe2x80x3 outer diameter drill pipe and 5xc2xdxe2x80x3 outer drill pipe in a single pipe trip, since the smaller cylindrical mandrel cannot be telescopingly received within the larger cylindrical mandrel. Moreover, in instances where the wall thickness of the outer testing mandrel must be reduced in order to permit the inner testing mandrel to be telescopingly received therein, the trength of the tool can also be greatly reduced resulting in a much greater risk that the tool could be pulled apart in the well. Further, the apparatus disclosed in Stockinger will permit testing of a maximum of two different size blowout preventers in a single pipe trip, and does not provide a means for safely and efficiently controlling a well when a kick is experienced during testing operations.
In summary, the prior art fails to disclose a method of testing or apparatus that can be used to test the pressure integrity of various size blowout preventers (including blowout preventers equipped with variable bore rams) against pipe having different yet very similar outer diameter dimensions, without making multiple trips in and out of a well, but which can also permit safe and efficient control of a well should a kick be experienced during testing operations. As illustrated more fully below, the present invention saves time and expense by providing a blowout preventer test tool that can permit the testing of multiple size blowout preventers in a single pipe trip, while also providing a means to safely and quickly shut in a well when necessary. Moreover, unlike telescoping blowout preventer test tools, the apparatus of the present invention permits the testing of blowout preventers against a number of pipes having different, yet very similar, outer diameter dimensions. Further, the present invention can withstand greater pulling forces than existing telescoping test tools, since there is no need to reduce the wall thickness of its various components.
The present invention relates to a method and apparatus for testing subsea blowout preventer assemblies that enables an operator to test various size blowout preventers, as well as variable bore rams, against pipe having different outer diameter dimensions on a single pipe trip. Furthermore, the apparatus of the present invention allows an operator to quickly and safely shut-in a well in the event that a kick is experienced during testing operations. The testing apparatus of the present invention generally comprises a plurality of elongated testing cylinders connected to a plurality of test seal assemblies, all of which are slidably received within a test plug having a bore therethrough. In its preferred embodiment, the testing apparatus of the present invention generally comprises the following elements: a plurality of elongated testing cylinders, each having a different outer diameter dimension; a plurity of test seal assemblies connected to said elongated testing cylinders and spaced between said elongated testing cylinders in alternating fashion; and a test plug having a bore therethrough which is slidably disposed on said elongated testing cylinders and test seal assemblies. Additionally, the testing apparatus of the present invention can also be equipped with a circulating test assembly to permit testing of pressure integrity of choke lines, kill lines and associated valves, as well as a side-port assembly, and a check-valve assembly.
The testing apparatus of the present invention is used to test the pressure integrity of a subsea blowout preventer assembly by lowering said testing apparatus into a well on drill pipe or other tubular work string. Although not absolutely required, it is generally preferable to attach an additional amount of work string, typically several hundred feet, to the bottom of the testing apparatus. The testing apparatus is then run into the well until the test plug is landed in a wellhead assembly which is situated immediately below a blowout preventer assembly to be tested. When properly landed within said wellhead assembly, the test plug forms a pressure-tight seal which seals off the wellbore. While it is envisioned that said test plug may seal directly against said wellhead, it is possible that the test plug may seal against a wear bushing or other apparatus within the wellhead. The lowermost test seal assembly is slidably disposed within the inner bore of the test plug; however, said lowermost test seal assembly is releasably locked in a stationary position within said test plug inner bore by a connector means when the testing apparatus is run into the well. When the test plug is landed within said wellhead assembly, the lowermost elongated testing cylinder is positioned in direct alignment with the blowout preventer assembly to be tested. In this position, individual blowout preventers are selectively closed against the outer circumference of said lowermost elongated testing cylinder, thereby defining an enclosed test zone between the test plug and the closed blowout preventer to be tested. Pressurized fluid is then introduced into said enclosed test zone utilizing the blowout preventer assembly choke or kill lines. In the event that the blowout preventer being tested fails to withstand the test pressure, then a satisfactory test will not be obtained and fluid flow will be observed at the surface from the well annulus. Alternatively, in the event that the blowout preventer withstands the test pressure but the test plug leaks, then fluid will pass around said test plug and enter the tubular work string situated below said testing apparatus. Under this scenario, a satisfactory test will not be obtained, and fluid flow will be observed at the surface from the work string.
After all desired testing under the aforementioned configuration (i.e., against said lowermost elongated testing cylinder) is complete, the lowermost test seal assembly can be releasably disconnected from the test plug. Once disconnected, transfer of weight to the testing apparatus via the tubular work string will permit downward movement of the lowermost test seal assembly and lowermost elongated test cylinder through the inner bore of the test plug. The testing apparatus can be shifted in this manner until a desired upper test seal assembly is concentrically positioned within the inner bore of the test plug, and a desired upper elongated testing cylinder having a different outer diameter than other elongated test cylinders of the testing apparatus is positioned in direct alignment with the blowout preventer assembly. Once the testing apparatus is shifted in this manner, additional components of the blowout preventer assembly can be closed against the outer circumference of said upper elongated testing cylinder, thereby defining an enclosed test zone between the test plug and the closed blowout preventer component being tested. Pressurized fluid can then be introduced into said enclosed test zone in order to test the pressure integrity of said blowout preventer component. After this testing is completed, the test tool can again be shifted, and the entire process can be repeated as desired for each elongated testing cylinder. The uppermost test seal assembly is prevented from passing through the inner bore of the test plug by a xe2x80x9cno-goxe2x80x9d shoulder located near the top of the uppermost test seal assembly. Additionally, the uppermost test seal assembly may also include a connector means to lock said uppermost test seal assembly in a stationary position within the inner bore of said test plug in a final shifted position. Thus, after all testing is completed, the work string can be pulled out of the well, and the entire test tool can be completely retrieved from the well bore.
Should a kick be experienced during testing operations, the entire test apparatus can be picked up via the work string and lifted to a position above the blowout preventer assembly. The well can then be shut in by closing one or more blowout preventers around tubular work string connected to the bottom of the testing apparatus. Necessary corrective action can then be taken to kill the well and restore said well to a controlled condition, including pumping through the work string.
It is an object of the present invention to provide a method for testing blowout preventer assemblies which permits the testing of multiple size blowout preventers in a single trip.
It is an object of the present invention to provide a blowout preventer test tool that permits testing of multiple size blowout preventers in a single pipe trip.
It is another object of the present invention to provide a blowout preventer test tool that permits testing of multiple size blowout preventers, as well as variable bore ram blowout preventers, against pipe having different outer diameter dimensions in a single pipe trip.
It is yet another object of the present invention to provide a blowout preventer test tool that permits testing of multiple size blowout preventers, as well as variable bore ram blowout preventers, against pipe having different yet very similar outer diameter dimensions in a single pipe trip.
It is another object of the present invention to provide a blowout preventer test tool that permits a well to be quickly and safely shut in should a kick be experienced during testing operations.
Other aspects, advantages and objects of the invention will become apparent to those skilled in the art upon reviewing the following detailed description, the drawings and appended claims.